The invention relates to a glass composition which is suitable for use primarily in electric lamps.
Certain glass parts of electric lamps, for example stems of incandescent and fluorescent lamps, furthermore bulbs of some fluorescent lamps have been manufactured from relatively high (20-29 mass %) lead oxide-containing (PbO) glasses for a long time. The high lead oxide content ensures the expected high electric resistance as well as the satisfactory softness and good workability of the glass material.
However, it is known that a high lead oxide-containing glass can adversely affect the environment both during glass/lamp production process and in the form of waste arising at the users. For reason of environment protection, decreasing or even eliminating the lead content from the mass products made from glasses containing lead oxide has to be sought after. A European patent application No. EP 603 933 describes a lead-free glass composition suitable for use in electric lamps. Although the technical characteristics of the glass compositions described in this patent application (e.g.: electric resistance, thermal expansion, etc.) are closely approaching those of the lead glass compositions, it is a serious disadvantage that they comprise barium oxide in 7 to 11 mass % in addition to the components (SiO.sub.2, Al.sub.2 O.sub.3, Na.sub.2 O, K.sub.2 O, Li.sub.2 O, CaO, MgO) usually applied in the glass compositions. The BaO is less harmful than the PbO taking into account the present regulations of environmental protection, nevertheless it still has a strong poisoning effect and its use has to be avoided owing to reasons of labor hygiene.